On Wed, Jul 06, 2022, Jue Wang wrote: > Fix an access to vcpu->arch.apic when KVM_X86_SETUP_MCE is called > without KVM_CREATE_IRQCHIP called or KVM_CAP_SPLIT_IRQCHIP is > enabled. > > Reported-by: https://syzkaller.appspot.com/bug?id=10b9b238e087a6c9bef2cc48bee2375f58fabbfc > > Fixes: 4b903561ec49 ("KVM: x86: Add Corrected Machine Check Interrupt (CMCI) emulation to lapic.") > Signed-off-by: Jue Wang <juew@xxxxxxxxxx> > --- > arch/x86/kvm/x86.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 4322a1365f74..5913f90ec3f2 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4820,8 +4820,9 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu, > if (mcg_cap & MCG_CMCI_P) > vcpu->arch.mci_ctl2_banks[bank] = 0; > } > - vcpu->arch.apic->nr_lvt_entries = > - KVM_APIC_MAX_NR_LVT_ENTRIES - !(mcg_cap & MCG_CMCI_P); > + if (lapic_in_kernel(vcpu)) > + vcpu->arch.apic->nr_lvt_entries = > + KVM_APIC_MAX_NR_LVT_ENTRIES - !(mcg_cap & MCG_CMCI_P); This is incomplete. If there's a "new" LVT entry, then it needs to be initialized (masked), and the APIC version needs to be updated to reflect the up-to-date number of LVT entries. This is what I came up with, again compile tested only, will formally post next week. From: Sean Christopherson <seanjc@xxxxxxxxxx> Date: Fri, 8 Jul 2022 15:48:10 -0700 Subject: [PATCH] KVM: x86: Fix handling of APIC LVT updates when userspace changes MCG_CAP Add a helper to update KVM's in-kernel local APIC in response to MCG_CAP being changed by userspace to fix multiple bugs. First and foremost, KVM needs to check that there's an in-kernel APIC prior to dereferencing vcpu->arch.apic. Beyond that, any "new" LVT entries need to be masked, and the APIC version register needs to be updated as it reports out the number of LVT entries. Fixes: 4b903561ec49 ("KVM: x86: Add Corrected Machine Check Interrupt (CMCI) emulation to lapic.") Reported-by: syzbot+8cdad6430c24f396f158@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: Siddh Raman Pant <code@xxxxxxxx> Cc: Jue Wang <juew@xxxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/lapic.c | 19 +++++++++++++++++++ arch/x86/kvm/lapic.h | 1 + arch/x86/kvm/x86.c | 4 ++-- 3 files changed, 22 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 1540d01ecb67..50354c7a2dc1 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -433,6 +433,25 @@ void kvm_apic_set_version(struct kvm_vcpu *vcpu) kvm_lapic_set_reg(apic, APIC_LVR, v); } +void kvm_apic_after_set_mcg_cap(struct kvm_vcpu *vcpu) +{ + int nr_lvt_entries = kvm_apic_calc_nr_lvt_entries(vcpu); + struct kvm_lapic *apic = vcpu->arch.apic; + int i; + + if (!lapic_in_kernel(vcpu) || nr_lvt_entries == apic->nr_lvt_entries) + return; + + /* Initialize/mask any "new" LVT entries. */ + for (i = apic->nr_lvt_entries; i < nr_lvt_entries; i++) + kvm_lapic_set_reg(apic, APIC_LVTx(i), APIC_LVT_MASKED); + + apic->nr_lvt_entries = nr_lvt_entries; + + /* The number of LVT entries is reflected in the version register. */ + kvm_apic_set_version(vcpu); +} + static const unsigned int apic_lvt_mask[KVM_APIC_MAX_NR_LVT_ENTRIES] = { [LVT_TIMER] = LVT_MASK, /* timer mode mask added at runtime */ [LVT_THERMAL_MONITOR] = LVT_MASK | APIC_MODE_MASK, diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index 762bf6163798..117a46df5cc1 100644 --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -99,6 +99,7 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value); u64 kvm_lapic_get_base(struct kvm_vcpu *vcpu); void kvm_recalculate_apic_map(struct kvm *kvm); void kvm_apic_set_version(struct kvm_vcpu *vcpu); +void kvm_apic_after_set_mcg_cap(struct kvm_vcpu *vcpu); bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source, int shorthand, unsigned int dest, int dest_mode); int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index fb37d11dec2d..801c3cfd3db5 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4893,8 +4893,8 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu, if (mcg_cap & MCG_CMCI_P) vcpu->arch.mci_ctl2_banks[bank] = 0; } - vcpu->arch.apic->nr_lvt_entries = - KVM_APIC_MAX_NR_LVT_ENTRIES - !(mcg_cap & MCG_CMCI_P); + + kvm_apic_after_set_mcg_cap(vcpu); static_call(kvm_x86_setup_mce)(vcpu); out: base-commit: 03d84f96890662681feee129cf92491f49247d28 --
